improved first half of Julia tutorial: reworded comments, added a few new tips, fixed a bug or two.
Revised Julia in Y Minutes, until Types section.
Expanded Type and Multiple Dispatch sections, and added more dispatch examples. Also added link to mailing list.
remove extraneous end
updated method names (add! -> push!, contains -> in)
updated date
Fix a couple forgotten references to `contains` in the comments
Merge pull request #389 from astrieanna/julia-revise

[julia/en] Revised Julia in Y Minutes